Separation of estrogens by micellar electrokinetic chromatography

Capillary electrophoresis of the sex hormone estrogens using different buffer components was investigated. Free zone electrophoresis with 10 mM phosphate buffer (pH 11.5) or 10 mM phosphate buffer with 10-20% methanol was not effective in separating the ten estrogens used in this study. However, nine estrogens were resolved by micellar electrokinetic chromatography using a 10 mM borate buffer (pH 9.2) containing 100 mM sodium cholate. In addition, some estrogens were partially separated using sodium dodecyl sulfate (SDS) micellar buffers; however, the addition of modifiers such as organic solvents or cyclodextrins improved resolutions significantly. Using a 10 mM phosphate buffer (pH 7.0) containing 50 mM SDS and 20% methanol, or a 10 mM borate buffer (pH 9.2) containing 50 mM SDS and 20 mM gamma-cyclodextrin, all ten of the tested estrogens were separated. However, the cyclodextrin-modified buffer allowed faster separation.